An effective categorization of test entries based on distinct characteristics is essential for distinguishing genetically similar and dissimilar genotypes, a fundamental requirement for any genetic study. The analysis of the variance indicated distinctions among the different genetic types across all traits under investigation.
Grouping of genotypes into clusters
Using Tocher’s method, 50 selected rice genotypes were divided into six distinct clusters as depicted in Table 1. The D
2 values were derived from the average of genotypes. The cluster dendrogram shows the variety of genotypes within the plant population studied (Fig 1). Among them, the total number of genotypes in Cluster I was highest (40), followed by Cluster II (4) and Cluster V (3). Clusters III (Barsha), V (NLR 9674) and VI (Tulaipanji) stood out as solitary clusters.
Kushwaha et al., (2020) and
Singh et al., (2022) found similar results about the non-association between geographical regions and genetic diversity. According to
Rezk et al., (2024) and
Sheeba et al., (2023), various traits contributed to genetic differences with no correlation observed between the origin of the genotypes and their genetic diversity.
Average intra and inter-cluster distances
The intra-cluster distances varied from zero (Clusters III, IV and VI) to 200.11 (Cluster V). The greatest inter-cluster distance (833.28) was observed between Cluster V and II followed by Cluster VI and V (499.65), Cluster VI and IV (462.52), Cluster IV and II (427.44), Cluster III and II (402.5) and Cluster VI and III (371.2) indicating substantial genetic diversity among genotypes across these clusters (Table 2 and Fig 2). Crosses from genotypes in Cluster I, II and V exhibiting significant divergence are likely to yield more favorable offspring for achieving increased yield through genetic diversity
(Chhodavadiya et al., 2023; Thakur and Sarma, 2023).
The analysis of genetically divergent clusters and the computation of distances (D
2 values) among the studied genotypes of rice are given in Table 3. Upon careful examination of these distances, it was observed that NLR 28523 in Cluster V and Khandagiri in Cluster II showed the highest genotypic distance (1742.78). Similar patterns of significant genetic distances between rice lines were identified in other clusters, such as Tulaipanji in Cluster VI and NLR 28523 in Cluster V (992.17). Tulaipanji in Cluster VI and NLR 9674 in Cluster IV demonstrated a considerable genotypic distance (627.20). Also, NLR 9674 in Cluster IV and Khandagiri in Cluster II exhibited a considerable genotypic distance (803.85). Additionally, Barsha in Cluster III and Khandagiri in Cluster II showed D2 distance (691.12) and Tulaipanji in Cluster VI and Barsha in Cluster III recorded a substantial genotypic distance (387.07). Identifying parental lines from these different groups has great potential for breeding programs. Crossing parents with greater genetic divergence can generate higher variability and strong beneficial traits in their offspring. These results were also in accordance with some previous studies
(Mondal et al., 2024; Roy et al., 2023;2024).
Cluster means
Table 4 shows the cluster means for DFF and DM, which were highest in Cluster IV (150.67 and 180.67) and lowest in Cluster II (96.08 and 126.33). Similarly, the cluster mean for PH was highest in Cluster III (158.26) and lowest in Cluster II (109.38). The NPT exhibited highest mean value in Cluster VI (20.33) and lowest in Cluster III (9.60), while PL had its highest mean in Cluster VI (27.00) and lowest in Clusters II and III (22.49). For TW, Cluster III (26.97) recorded highest mean, while Cluster V (16.26) had lowest. The highest mean for TGP was in Cluster V (240.60), whereas lowest was in Cluster II (96.28). Cluster V (202.99) exhibited highest mean for FGP, whereas Cluster VI (53.27) had lowest. SF had the maximum mean in Cluster II (97.44) and Cluster III (60.57) had minimum value. GYP and BYP had highest mean in Cluster IV (36.31 and 84.86) and lowest in Cluster VI (20.03 and 46.10). HI and LB had highest mean in Cluster II (4.45 and 0.52) and lowest in Cluster IV (2.78 and 0.43). GL had highest mean in Cluster II (9.85) and lowest in Cluster V (6.68), while GB had highest mean in Cluster III (2.69) and lowest mean in Cluster VI (1.92). Cluster IV (48.55) exhibited highest mean for SYP, whereas Cluster II (22.28) showed lowest mean. The findings demonstrated significant genetic divergence within the genotypes in these groups, suggesting their potential utility in targeted trait enhancement in plant breeding initiatives. Crossing genotypes within these clusters is also expected to produce substantial heterosis. This result aligns with earlier studies by
Pavankumar et al., (2022) and
Sudeepthi et al., (2020).
Contribution towards total divergence
The highest percentage contribution towards genetic divergence was observed in GYP (16.78%), followed by BYP (10.43%), TW (8.9%), PH (8.49%), HI (7.43%), SYP (7.33%), PL (6.42%), NPT (6.33%), SF (4.98%), GL (4.32%), LB (3.5%), GB (3.44%), FGP (3.43%), DFF (3.21%), DM (2.57%) and TGP (2.44%), as shown in Table 5 and Fig 3. All genotypes exhibited significant variability in economic traits especially in GYP suggesting the need for further study on allelic characterization. Previous studies also found similar results by different researchers
(Bhargavi et al., 2023; Bora et al., 2023; Shrivastav et al., 2022).
Principal component analysis
Principal component analysis serves to condense large datasets into more manageable principal components, preserving all crucial details by analyzing the correlations between variables. The eigenvector values, variation percentages and cumulative percentages are presented in Table 6. Among the eleven components, five PCs observed eigenvalues surpassing 1.0, thus contributing significantly to the cumulative variability of 84.72% across the considered variables. PC
1, accounting for 36.97% of the total variation, along with the rest of PCs, contributed 56.05%, 67.52%, 78.15% and 84.72% to the overall variance. Components boasting multiple eigenvalues showcased heightened variability among rice genotypes, facilitating the identification of diverse parental selections. The scree plot provided insights into the percentage of variance explained by eigenvalues and principal components (Fig 4). In this study, PC
1 showed 36.97% variability, characterized by an eigenvalue of 5.92. The graph depicts PC
1 as exhibiting the highest degree of variability compared to other PCs. One earlier research reported a maximum variance of 38.72% in PC
1 across 49 rice lines
(Christina et al., 2021). Thus, selecting genotypes from PC
1 could prove advantageous for future breeding endeavors focused on improving traits
(Tiwari et al., 2022).
In this study, the biplot is constructed using PC
1 and PC
2 to analyze the associations between 50 rice accessions based on yield and its related attributes (Fig 5). Biplot based correlations among traits explained 56.05% of the total variation, providing a reliable estimate for evaluating their impact on yield and inter-similarities. All characters except TGP, SF, NPT and HI have higher vector lengths, indicating a more substantial influence on the variation in a particular dimension. The loading plot revealed substantial diversity among nearly all genotypes and variables. These findings are consistent with those reported by
Sheela et al., (2020).
The contribution of 16 quantitative traits to the principal components is presented in Table 7. In PC
1, SYP (0.913) followed by BYP (0.908), DM (0.890), DFF (0.881), GYP (0.780), FGP (0.763), PH (0.556), TGP (0.500), GB (0.441), PL (0.300) and SF (0.184) showed favourable loadings, while the remaining traits exhibited negative loadings. PC
2 showed positive loadings for parameters such as TW (0.888), GL (0.754), NPT (0.484) and HI (0.434) with other factors such as FGP (-0.493) followed by SF (-0.416) and TGP (-0.194) demonstrating negative loadings. Traits in PC
3 that recorded positive loadings were LB (0.579), SF (0.572), NPT (0.417), SYP (0.301), GL (0.292), BYP (0.203), DFF (0.120), DM (0.111) and GYP (0.043), while the remaining characters observed negative loadings. In PC
4, variables such as PL (0.613), NPT (0.448), TGP (0.415), PH (0.332), LB (0.126) and SYP (0.026) exhibited positive loading values and the remaining traits showed negative loadings. In PC
5, TGP (0.502) followed by LB (0.398), FGP (0.287) and GL (0.258) exhibited positive loadings, while PH (-0.418), followed by GB (-0.295), SF (-0.228) and NPT (-0.148) showed negative loadings. Among the studied traits, PC
1 and PC
2 contributed more to genetic divergence and accounted for a significant portion of the variability. Therefore, selecting traits with substantial variability will benefit future breeding endeavors.